The present invention relates to vent cap assemblies for liquid transport tanks and, more particularly, to a vent cap assembly which minimizes leakage but allows venting of the liquid holding tank of a tanker truck.
The prior art has exhibited numerous types of caps for tank trucks which seal the contents of a tanker truck. For certain types of cargoes, for example in hauling juices, milk and the like, it is desirable that a cap not only prevent leakage of the contents, but provide venting of the liquid holding container of the tank truck. Certain types of caps have been designed to relieve internal pressure inside of a holding container when the pressure exceeds a predetermined level. For example, a cap having a venting aperture can be sealed by a spring loaded member which exposes the venting aperture to a venting flow path when the internal pressure of the tank exceeds the spring force exerted on the cap. (See U.S. Pat. No. 3,927,798.) Degassifying valves for relieving pressure of tankers containing dangerous or combustible liquids have also used spring-loaded sealing mechanisms. (See U.S. Pat. No. 4,624,286.)
In the liquid food transport industry, it is desirable that the liquid container of a transport vehicle be allowed to breathe while preventing leakage of the contents. Leakage or spillage can occur from sloshing on rough roads or when making turns if means are not provided to retain the liquid in the container. One concept which has been demonstrated is that of a venting member which is to be inserted into an access opening of a transport tank. The venting member is provided with horizontally extending baffles which are braced by a center rod and which are vertically spaced from one another in a staggered, overlapping relationship to allow an airflow path to extend from interior of the liquid holding tank to the exterior of the tank truck. (See U.S. Pat. Nos. 4,127,216 and 4,081,107.)
As shown in the above noted patents, the trend in the industry is toward more complicated devices requiring time-consuming maintenance for keeping the sealing and venting devices clean, which of course is desirable in the liquid food hauling industry. Therefore, a need is seen for a simple and effective sealing and venting device which is easily maintained and cleaned.